Apache Ant™ in Anger:

Using Apache Ant in a Production Development System

Steve Loughran
Last updated 2005-03-16

Apache Ant
can be an invaluable tool in a team development process - or it can
be yet another source of problems in that ongoing crises we call
development . This
document contains some strategies and tactics for making the most of
Ant. It is moderately frivolous in places, and lacks almost any actual
examples of Ant XML. The lack of examples is entirely deliberate - it
keeps document maintenance costs down. Most of the concepts covered
don't need the detail provided by XML representations, as it is the processes we
are concerned about, not the syntax. Finally, please be aware that the
comments here are only suggestions which need to be customised to meet
your own needs, not strict rules about what should and should not be
done.

Firstly, here are some assumptions about the projects which this
document covers:

Pretty much pure Java, maybe with some legacy cruft on the edges.

Team efforts, usually with the petulant prima-donnas all us Java
programmers become once we realise how much in demand we are.

A fairly distributed development team - spread across locations and
maybe time zones.

Separate sub projects - from separate beans in a big
enterprise application to separate enterprise applications which need to
be vaguely aware of each other.

Significant mismatch between expectations and time available to
deliver. 'Last Week' is the ideal delivery date handed down from above,
late next century the date coming up from below.

Everyone is struggling to keep up with platform and tool evolution.

Extensive use of external libraries, both open and closed source.

What that all means is that there is no time to spend getting things
right, you don't have that tight control on how the rest of the team
works and the development process is often more one of chaos minimisation
than anything else. The role of Ant in such projects is to ensure that
the build, test and deploy processes run smoothly, leaving you with all
the other problems.

Clarify what you want Ant to do

Ant is not a silver bullet. It is just another rusty bullet in the armory of
development tools available at your disposal. Its primary purpose is to
accelerate the construction and deployment of Java projects. You could certainly
extend Ant to do anything Java makes possible: it is easy to imagine writing an
image processing task to help in web site deployment by shrinking and
recompressing jpeg files, for example. But that would be pushing the boundary of
what Ant is really intended to do - so should be considered with care.

Ant is also a great adjunct to an IDE; a way of doing all the housekeeping of
deployment and for clean, automated builds. But a good modern IDE is a
productivity tool in its own right - one you should continue to use. Ant
just lets you give the teams somewhat more freedom in IDE choice - "you can
use whatever you want in development, but Ant for the deployment
builds" Now that many modern open source and commercial IDEs
include Ant support (including jEdit, Forte, Eclipse and IDEA),
developers can use a great IDE, with Ant providing a rigorous and portable
build process integrated into the tool.

Define standard targets

When you have multiple sub projects, define a standard set of targets.
Projects with a split between interface and implementation jar files
could consider impl and intf targets - with separate
debug-impl and debug-intf targets for the debug version.
And of course, the ubiquitous clean target.

With standard target names, it is easy to build encompassing Ant build
files which just hand off the work to the classes below using the
ant
task. For example. the clean target could be handed down to the intf and
impl subdirectories from a parent directory

If you give targets a description tag, then calling ant
-projecthelp will list all tasks with their description as 'main targets', and
all tasks without a description as subtargets. Describing all your
entry points is therefore very useful, even before a project becomes big and complicated.

Extend Ant through new tasks

If Ant does not do what you want, you can use the
exec and
java tasks or
inline scripting to extend it. In a
project with many build.xml files, you soon find that having a single
central place for implementing the functionality keeps maintenance
overhead down. Implementing task extensions through Java code seems
extra effort at first, but gives extra benefits:-

Cross platform support can be added later without changing any
build.xml files

The code can be submitted to the Ant project itself, for other
people to use and maintain

It keeps the build files simpler

In a way, it is this decoupling of functionality, "the tasks", from
the declaration of use, "the build file", that has helped Ant succeed.
If you have to get something complex done in Make or an IDE, you have a
hairy makefile that everyone is scared of, or an IDE configuration that
is invariably very brittle. But an Ant task is reusable and shareable
among all Ant users. Many of the core and optional tasks in Ant today,
tasks you do or will come to depend on, were written by people trying to
solve their own pressing problems.

Embrace Automated Testing

(alternatively "recriminate early, recriminate often")

Ant lets you call JUnit
tasks, which unit test the code your team has written. Automated testing
may seem like extra work at first, but JUnit makes writing unit tests so
easy that you have almost no reason not to. Invest the time in learning
how to use JUnit, write the test cases, and integrate them in a 'test'
target from Ant so that your daily or hourly team build can have the
tests applied automatically. One of the free to download chapters of
Java Development with Ant
shows you how to use JUnit from inside Ant.

Once you add a way to fetch code from the SCM system, either as an Ant
task, in some shell script or batch file or via some continuous
integration tool. the integration test code can be a pure Ant task run
on any box dedicated to the task. This is ideal for verifying that the
build and unit tests work on different targets from the usual
development machines. For example, a Win95/Java1.1 combination could be
used even though no developer would willingly use that configuration
given the choice.

System tests are harder to automate than unit tests, but if you can
write java code to stress large portions of the system - even if the code
can not run as JUnit tasks - then the java
task can be used to invoke them. It is best to specify that you want a
new JVM for these tests, so that a significant crash does not break the
full build. The Junit extensions such as
HttpUnit for web pages, and
Cactus for J2EE and servlet
testing help to expand the testing framework. To test properly you will still
need to invest a lot of effort in getting these to work with your project, and
deriving great unit, system and regression tests - but your customers will love
you for shipping software that works.

Learn to Use and love the add-ons to Ant

The Ant distribution is not the limit of the Ant universe, it is only
the beginning. Look at the
External Tools and Tasks page
for an up to date list. Here are some of them that .

Checkstyle
This tool audits your code and generates HTML reports of wherever any
style rule gets broken. Nobody can hide from the code police now! tip:
start using this early, so there's less to correct.

Ant-contrib
This sourceforge project contains helper tasks that are kept separate
from core Ant for ideological purity; the foreach and trycatch tasks in
particular. These give you iteration and extra error handling. Also on
the site is the <cc> task suite, that compile and link native code
on a variety of platforms.

XDoclet
XDoclet adds attributed oriented programming to Java. By adding javadoc
tags to your code you can have XDoclet automatically generate web.xml
descriptors, taglib descriptors, EJB interfaces, JMX interface classes,
Castor XML/SQL bindings, and many more. The key here is that all those
fiddly little XML files you need to create, and those interfaces EJB and
JMX requires to implement, all can be autogenerated from your Java
code with a few helper attributes. This reduces
errors and means you can change your code and have the rest of the app
take its cue from the source. Never do EJB, JMX or webapps without it!

Ant is the best foundation for cross platform Java development and
testing to date. But if you are not paying attention, it is possible to
produce build files which only work on one platform - or indeed, one
single workstation.

The common barriers to cross-platform Ant are the use of command line
tools (exec tasks) which are not portable, path issues, and hard coding
in the location of things.

The trouble with external invocation is that not all functions are found
cross platform, and those that are often have different names - DOS
descendants often expect .exe or .bat at the end of files. That can be
bad if you explicitly include the extension in the naming of the command
(don't!), good when it lets you keep the unix and DOS versions of an
executable in the same bin directory of the project without name
clashes arising.

Both the command line invocation tasks let you specify which platform
you want the code to run on, so you could write different tasks for each
platform you are targeting. Alternatively, the platform differences
could be handled inside some external code which Ant calls. This can be
some compiled down java in a new task, or an external script file.

Cross platform paths

Unix paths use forward slashes between directories and a colon to
split entries. Thus
"/bin/java/lib/xerces.jar:/bin/java/lib/ant.jar" is
a path in unix. In Windows the path must use semicolon separators,
colons being used to specify disk drives, and backslash separators
"c:\bin\java\lib\xerces.jar;c:\bin\java\lib\ant.jar".

This difference between platforms (indeed, the whole java classpath
paradigm) can cause hours of fun.

Ant reduces path problems; but does not eliminate them entirely. You
need to put in some effort too. The rules for handling path names are
that 'DOS-like pathnames are handled', 'Unix like paths are handled'.
Disk drives -'C:'- are handled on DOS-based boxes, but placing them in
the build.xml file ruins all chances of portability. Relative file paths
are much more portable. Semicolons work as path separators - a fact which
is useful if your Ant invocation wrapper includes a list of jars as a
defined property in the command line. In the build files you may find it
better to build a classpath by listing individual files (using location=
attributes), or by including a fileset of *.jar in the classpath
definition.

There is also the PathConvert task which
can put a fully resolved path into a property. Why do that? Because then
you can use that path in other ways - such as pass it as a parameter to
some application you are calling, or use the replace task to patch it
into a localised shell script or batch file.

Note that DOS descended file systems are case insensitive (apart from
the obscure aberration of the WinNT POSIX subsystem run against NTFS),
and that Windows pretends that all file extensions with four or more
letters are also three letter extensions (try DELETE *.jav in your java
directories to see a disastrous example of this).

Ant's policy on case sensitivity is whatever the underlying file system
implements, and its handling of file extensions is that *.jav does not
find any .java files. The Java compiler is of course case sensitive - you can
not have a class 'ExampleThree' implemented in "examplethree.java".

Some tasks only work on one platform -
Chmod being a classic example. These tasks usually result in just a
warning message on an unsupported platform - the rest of the target's
tasks will still be called. Other tasks degrade their functionality on
platforms or Java versions. In particular, any task which adjusts the
timestamp of files can not do so properly on Java 1.1. Tasks which can
do that - Get, Touch and
Unjar/Unwar/Unzip for example, degrade their functionality on
Java1.1, usually resorting to the current timestamp instead.

Finally, Perl makes a good place to wrap up Java invocations cross
platform, rather than batch files. It is included in most Unix
distributions, and is a simple download for Win32 platforms from
ActiveState. A Perl file with .pl extension, the usual Unix
path to perl on the line 1 comment and marked as executable can be run
on Windows, OS/2 and Unix and hence called from Ant without issues. The
perl code can be left to resolve its own platform issues. Don't forget to
set the line endings of the file to the appropriate platform when you
redistribute Perl code; fixCRLF
can do that for you.

Even if each team member is allowed their choice of IDE/editor, or even
OS, you need to set a baseline of functionality on each box. In
particular, the JDKs and jars need to be in perfect sync. Ideally pick
the latest stable Java/JDK version available on all developer/target
systems and stick with it for a while. Consider assigning one person to
be the contact point for all tools coming in - particularly open source
tools when a new build is available on a nightly basis. Unless needed,
these tools should only really be updated monthly, or when a formal
release is made.

Another good tactic is to use a unified directory tree, and add on extra
tools inside that tree. All references can be made relative to the tree.
If team members are expected to add a directory in the project to their
path, then command line tools can be included there - including those
invoked by Ant exec tasks. Put everything under source code control and
you have a one stop shop for getting a build/execute environment purely
from CVS or your equivalent.

One big difference between Ant and older tools such as Make is that the
processes for deploying Java to remote sites are reasonably well
evolved in Ant. That is because we all have to do it these days, so
many people have put in the effort to make the tasks easier.

Ant can Jar, Tar or Zip files for deployment, while the
War task extends the jar task
for better servlet deployment.
Jlink is a
jar generation file which lets you merge multiple sub jars. This is
ideal for a build process in which separate jars are generated by sub
projects, yet the final output is a merged jar. Cab can be used on Win32 boxes to
build a cab file which is useful if you still have to target IE deployment.

The ftp task lets you move stuff up to a
server. Beware of putting the ftp password in the build file - a property
file with tight access control is slightly better. The FixCRLF task is often a useful interim step if
you need to to adjust the line endings of files. A
WebDav task has long been discussed, which would provide a more secure
upload to web servers, but it is still in the todo list. Rumour has it
that there is such a task in the jakarta-slide libraries. With MacOS X,
Linux and Windows XP all supporting WebDAV file systems, you may even be able
to use copy to deploy
though a firewall.

EJB deployment is aided by the ejb tasks,
while the
serverdeploy
suite can deploy to multiple servers. The popularity of Ant has
encouraged vendors to produce their own deployment tasks which they
redistribute with their servers. For example, the Tomcat4.1 installation
includes tasks to deploy, undeploy and reload web applications.

Finally, there are of course the fallbacks of just copying files to a
destination using Copy and Copydir , or just sending them to a person or
process using Mail or the attachment
aware MimeMail.
In one project our team even used Ant to build CD images through a build followed
by a long set of Copy tasks, which worked surprisingly well, certainly
easier than when we mailed them to the free email service on
myrealbox.com, then pulled them down from the far end's web browser, which we
were running over WinNT remote desktop connection, that being tunneled
through SSH.

How you structure your directory tree is very dependent upon the
project. Here are some directory layout patterns which can be used as
starting points. All the jakarta projects follow a roughly similar
style, which makes it easy to navigate around one from one project to
another, and easy to clean up when desired.

Simple Project

The project contains sub directories

bin

common binaries, scripts - put this on the path.

build

This is the tree for building; Ant creates it and can empty it
in the 'clean' project.

dist

Distribution outputs go in here; the directory is created in Ant
and clean empties it out

doc

Hand crafted documentation

lib

Imported Java libraries go in to this directory

src

source goes in under this tree in a hierarchy which matches
the package names. The dependency rules of <javac> requires this.

The bin, lib, doc and src directories should be under source code control.
Slight variations include an extra tree of content to be included in the
distribution jars - inf files, images, etc. These can go under source
too, with a metadata directory for web.xml and similar
manifests, and a web folder for web content - JSP, html, images
and so on. Keeping the content in this folder (or sub hierarchy)
together makes it easier to test links before deployment. The actual
production of a deployment image, such as a war file, can be left to the
appropriate Ant task: there is no need to completely model your source tree
upon the deployment hierarchy.

Javadoc output can be
directed to a doc/ folder beneath build/, or to doc/javadoc.

Interface and Implementation split

If the interface is split from the implementation code then this can be
supported with minor changes just by having a separate build path for
the interface directory - or better still just in the jar construction:
one jar for interface and one jar for implementation.

Loosely Coupled Sub Projects

In the loosely coupled approach multiple projects can have their own
copy of the tree, with their own source code access rights.
One difference to consider is only having one instance of the bin and
lib directories across all projects. This is sometimes good - it helps
keep copies of xerces.jar in sync, and sometimes bad - it can update
foundational jar files before unit testing is complete.

To still have a single build across the sub projects, use parent
build.xml files which call down into the sub projects.

This style works well if different teams have different code
access/commitment rights. The risk is that by giving extra leeway to the
sub projects, you can end up with incompatible source, libraries, build
processes and just increase your workload and integration grief all round.

The only way to retain control over a fairly loosely integrated
collection of projects is to have a fully automated build
and test process which verifies that everything is still compatible. Sam
Ruby runs one for all the apache java libraries and emails everyone when
something breaks; your own project may be able to make use of
Cruise Control for
an automated, continuous, background build process.

Integrated sub projects

Tightly coupled projects have all the source in the same tree; different
projects own different subdirectories. Build files can be moved down to
those subdirectories (say src/com/iseran/core and src/com/iseran/extras),
or kept at the top - with independent build files named core.xml and
extras.xml.

This project style works well if everyone trusts each other and the
sub projects are not too huge or complex. The risk is that a split to a
more loosely coupled design will become a requirement as the projects
progress - but by the time this is realised schedule pressure and
intertwined build files make executing the split well nigh impossible.
If that happens then just keep with it until there is the time to
refactor the project directory structures.

Once you start using Ant, you should have a policy on when and how the
team updates their copies. A simple policy is "every official release
after whatever high stress milestone has pushed all unimportant tasks
(like sleep and seeing daylight) on the back burner". This insulates you
from the changes and occasional instabilities that Ant goes through
during development. Its main disadvantage is that it isolates you from
the new tasks and features that Ant is constantly adding.

Often an update will require changes to the build.xml files. Most
changes are intended to be backwards compatible, but sometimes an
incompatible change turns out to be
necessary. That is why doing the update in the lull after a big
milestone is important. It is also why including ant.jar and related
files in the CVS tree helps ensure that old versions of your software
can be still be built.

The most aggressive strategy is to get a weekly or daily snapshot of the
ant source, build it up and use it. This forces you to tweak the
build.xml files more regularly, as new tasks and attributes can take
while to stabilise. You really have to want the new features, enjoy
gratuitous extra work or take pleasure in upsetting your colleagues to
take this approach.

Once you start extending Ant with new tasks, it suddenly becomes much
more tempting to pull down regular builds. The most recent Ant builds
are invariably the best platform for writing your extensions, as you
can take advantage of the regular enhancements to the foundational
classes. It also prevents you from wasting time working on something
which has already been done. A newly submitted task to do something
complex such as talk to EJB engines, SOAP servers or just convert a text
file to uppercase may be almost exactly what you need - so take it,
enhance it and offer up the enhancements to the rest of the world. This
is certainly better than starting work on your 'text case converter'
task on Ant 0.8 in isolation, announcing its existence six months later
and discovering that instead of adulation all you get are helpful
pointers to the existing implementation. The final benefit of being
involved with the process is that it makes it easier for your tasks to
be added with the Ant CVS tree, bringing forward the date when Ant has
taken on all the changes you needed to make to get your project to work.
If that happens you can revert to an official Ant release, and get on
with all the other crises.

You should also get on the dev mailing list
, as it is where the other developers post their work, problems and
experience. The volume can be quite high: 40+ messages a day, so
consider routing it to an email address you don't use for much else. And
don't make everyone on the team subscribe; it can be too much of a
distraction.

Because Ant can read environment variables, copy, unzip and delete files
and make java and OS calls, it can be used for simple installation
tasks. For example, an installer for tomcat could extract the
environment variable TOMCAT_HOME, stop tomcat running, and copy a war
file to TOMCAT_HOME/webapps. It could even start tomcat again, but the
build wouldn't complete until tomcat exited, which is probably not what
was wanted.

The advantage of using Ant is firstly that the same install targets
can be used from your local build files (via an ant invocation
of the install.xml file), and secondly that a basic install target is
quite easy to write. The disadvantages of this approach are that the
destination must have an up to date version of Ant correctly
pre-installed, and Ant doesn't allow you to handle failures well - and a
good installer is all about handling when things go wrong, from files
being in use to jar versions being different. This means that Ant is not
suited for shrink wrapped software, but it does work for deployment and
installation to your local servers.

One major build project I was involved in had an Ant install build file
for the bluestone application server, which would shutdown all four
instances of the app server on a single machine, copy the new version of
the war file (with datestamp and buildstamp) to an archive directory,
clean up the current deployed version of the war and then install the
new version. Because bluestone restarted JVMs on demand, this script was
all you needed for web service deployment. On the systems behind the
firewall, we upped the ante in the deployment process by using the ftp
task to copy out the war and build files, then the telnet task to
remotely invoke the build file. The result was we had automated
recompile and redeploy to local servers from inside our IDE (Jedit) or
the command line, which was simply invaluable. Imagine pressing a button
on your IDE toolbar to build, unit test, deploy and then functional test
your webapp.

One extra trick I added later was a junit test case to run through the
install check list. With tests to verify access permissions on network
drives, approximate clock synchronisation between servers, DNS
functionality, ability to spawn executables and all the other trouble
spots, the install script could automatically do a system health test
during install time and report problems. [The same tests could also be
invoked from a JMX MBean, but that's another story].

So, Ant is not a substitute for a real installer tool, except in the
special case of servers you control, but in that context it does let
you integrate remote installation with your build.

The get task can fetch any URL, so be used
to trigger remote server side code during the build process, from remote
server restarts to sending SMS/pager messages to the developer
cellphones.

i18n

Internationalisation is always trouble. Ant helps here with the native2ascii task which can escape out all non
ascii characters into unicode. You can use this to write java files
which include strings (and indeed comments) in your own non-ASCII
language and then use native2ascii to convert to ascii prior to feeding
through javac. The rest of i18n and l12n is left to you...

Use Property Files

Use external property files to keep per-user settings out the build
files - especially passwords. Property files can also be used to
dynamically set a number of properties based on the value of a single
property, simply by dynamically generating the property filename from the
source property. They can also be used as a source of constants across
multiple build files.

Faster compiles with Jikes

The jikes compiler is usually much
faster than javac, does dependency checking and has better error
messages (usually). Get it. Then set
build.compiler to "jikes" for it to be used in your build files.
Doing this explicitly in your build files is a bit dubious as it requires the
whole team (and sub projects) to be using jikes too - something you can only
control in small, closed source projects. But if you set
ANT_OPTS = -Dbuild.compiler=jikes
in your environment, then all your builds on your system will use
Jikes automatically, while others can choose their own compiler, or let
ant choose whichever is appropriate for the current version of Java.

#include targets to simplify multi build.xml projects

You can import XML files into a build file using the XML parser itself.
This lets a multi-project development program share code through reference,
rather than cut and paste re-use. It also lets one build up a file of
standard tasks which can be reused over time. Because the import
mechanism is at a level below which Ant is aware, treat it as
equivalent to the #include mechanism of the 'legacy' languages C and
C++.

There are two inclusion mechanisms, an ugly one for all parsers and a
clean one. The ugly method is the only one that was available on Ant1.5 and
earlier:-

The cleaner method in Ant1.6 is the <import> task that imports
whole build files into other projects. The entity inclusion example
could almost be replaced by two import statements:-

<import file="propertiesAndPaths.xml">
<import file="taskdefs.xml">

We say almost as top level declarations (properties and taskdefs)
do not get inserted into the XML file exactly where the import statement
goes, but added to the end of the file. This is because the import process
takes place after the main build file is parsed, during execution, whereas
XML entity expansion is handled during the parsing process.

The <import> task does powerful things, such as let you override targets,
and use ant properties to name the location of the file to import. Consult the
documentation for the specifics of
these features.

Before you go overboard with using XML inclusion, note that the
ant task lets you call any target in any other build
file - with all your property settings propagating down to that target.
So you can actually have a suite of utility targets
- "deploy-to-stack-a", "email-to-team", "cleanup-installation" which can
be called from any of your main build files, perhaps with subtly changed
parameters. Indeed, after a couple of projects you may be able to create
a re-usable core build file which contains the core targets of a basic
Java development project - compile, debug, deploy - which project specific
build files call with their own settings. If you can achieve this then
you are definitely making your way up the software maturity ladder. With
a bit of work you may progress from being a SEI CMM Level 0 organisation
"Individual Heroics are not enough" to SEI CMM Level 1, "Projects only
succeed due to individual heroics"

NB, ant copies all your properties unless the
inheritall attribute is set to false. Before that attribute
existed you had to carefully name all property definitions in all build
files to prevent unintentional overwriting of the invoked property by
that of the caller, now you just have to remember to set
inheritall="false" on all uses of the <ant> task.

Implement complex Ant builds through XSL

XSLT can be used to dynamically generate build.xml files from a source
xml file, with the xslt task controlling
the transform. This is the current recommended strategy for creating
complex build files dynamically. However, its use is still apparently
quite rare - which means you will be on the bleeding edge of technology.

Change the invocation scripts

By writing your own invocation script - using the DOS, Unix or Perl
script as a starting point - you can modify Ant's settings and behavior for an
individual project. For example, you can use an alternate variable to
ANT_HOME as the base, extend the classpath differently, or dynamically
create a new command line property "project.interfaces" from all .jar
files in an interfaces directory.

Having a custom invocation script which runs off a CVS controlled
library tree under PROJECT_HOME also lets you control Ant versions
across the team - developers can have other copies of Ant if they want,
but the CVS tree always contains the jar set used to build your project.

You can also write wrapper scripts which invoke the existing Ant
scripts. This is an easy way to extend them. The wrapper scripts can add
extra definitions and name explicit targets, redefine ANT_HOME and
generally make development easier. Note that "ant" in Windows is really
"ant.bat", so should be invoked from another batch file with a "CALL
ant" statement - otherwise it never returns to your wrapper.

Write all code so that it can be called from Ant

This seems a bit strange and idealistic, but what it means is that you should
write all your java code as if it may be called as a library at some point in
future. So do not place calls to System.exit() deep in the code - if you
want to exit a few functions in, raise an exception instead and have
main() deal with it.

Moving one step further, consider proving an Ant Task interface to the
code as a secondary, primary or even sole interface to the
functionality. Ant actually makes a great bootloader for Java apps as it
handles classpath setup, and you can re-use all the built in tasks for
preamble and postamble work. Some projects, such as
XDoclet only run under Ant, because
that is the right place to be.

Use the replace task to programmatic modify text files in your project.

Imagine your project has some source files - BAT files, ASPX pages(!), anything
which needs to be statically customised at compile time for particular
installations, such driven from some properties of the project such as JVM options, or the URL
to direct errors too. The replace task can be used to modify files, substituting text and creating
versions customised for that build or destination. Of course, per-destination customisation
should be delayed until installation, but if you are using Ant for the remote installation
that suddenly becomes feasible.

Use the mailing lists

There are two
mailing lists
related to Ant, user and developer. Ant user is where all
questions related to using Ant should go. Installation, syntax, code
samples, etc - post your questions there or search the archives for
whether the query has been posted and answered before. Ant-developer
is where Ant development takes place - so it is not the place to
post things like "I get a compilation error when I build my project" or
"how do I make a zip file". If you are actually extending Ant, on the other
hand, it is the ideal place to ask questions about how to add new tasks, make
changes to existing ones - and to post the results of your work, if you want them
incorporated into the Ant source tree.

What does an Ant build process look like in this world? Assuming a
single directory structure for simplicity, the build file
should contain a number of top level targets

build - do an (incremental) build

test - run the junit tests

clean - clean out the output directories

deploy - ship the jars, wars, whatever to the execution system

publish - output the source and binaries to any distribution site

fetch - get the latest source from the cvs tree

docs/javadocs - do the documentation

all - clean, fetch, build, test, docs, deploy

main - the default build process (usually build or build & test)

Sub projects "web", "bean-1", "bean-2" can be given their own build
files - web.xml, bean-1.xml, bean-2.xml - with the same entry points.
Extra toplevel tasks related to databases, web site images and the like
should be considered if they are part of the process.

Debug/release switching can be handled with separate initialisation
targets called before the compile tasks which define the appropriate
properties. Antcall is the trick here, as it allows you to have two paths
of property initialisation in a build file.

You then have dependent targets, such as "compile", depend on this
conditional target; there the "default" properties are set, and then the
property is actually used. Because Ant properties are immutable,
if the release target was executed its settings will override the
default values:

As a result, we now have a build where the release mode only includes
the filename and line debug information (useful for bug reports), while
the development system included variables too.

It is useful to define a project name property which can be echoed in
the init task. This lets you work out which Ant file is breaking in a
multi file build.

What goes in to the internal Ant tasks depends on your own projects. One
very important tactic is "keep path redefinition down through
references" - you can reuse paths by giving them an ID and then
referring to them via the "refid" attribute you should only need to
define a shared classpath once in the file; filesets can be reused
similarly.

Once you have set up the directory structures, and defined the Ant tasks
it is time to start coding. An early priority must be to set up the
automated test process, as that not only helps ensures that the code
works, it verifies that the build process is working.

And that's it. The build file shouldn't need changing as new source
files get added, only when you want to change the deliverables or part
of the build process. At some point you may want to massively
restructure the entire build process, restructuring projects and the
like, but even then the build file you have should act as a foundation
for a split build file process -just pull out the common properties into
a properties file all build files read in, keep the target names unified
and keep going with the project. Restructuring the source code control
system is often much harder work.

The Limits of Ant

Before you start adopting Ant as the sole mechanism for the build
process, you need to be aware of what it doesn't do.

It's not a scripting language

Ant lets you declare what you want done, with a bit of testing of the
platform and class libraries first to enable some platform specific
builds to take place. It does not let you specify how to handle things
going wrong (a listener class can do that), or support complex
conditional statements.

If your build needs to handle exceptions then look at the sound listener
as a simple example of how to write your own listener class. Complex
conditional statements can be handled by having something else do the
tests and then build the appropriate Ant task. XSLT can be used for
this.

It's not Make

Some of the features of make, specifically inference rules and
dependency checking are not included in Ant. That's because they are
"different" ways of doing a build. Make requires you to state
dependencies and the build steps, Ant wants you to state tasks and the
order between them, the tasks themselves can do dependency checking or
not. A full java build using Jikes is so fast that dependency checking
is relatively moot, while many of the other tasks (but not all), compare
the timestamp of the source file with that of the destination file
before acting.

It's not meant to be a nice language for humans

XML isn't a nice representation of information for humans. It's a
reasonable representation for programs, and text editors and source code
management systems can all handle it nicely. But a complex Ant file can
get ugly because XML is a bit ugly, and a complex build is, well,
complicated. Use XML comments so that the file you wrote last month
still makes sense when you get back to it, and use proper xml editors to edit the
files if you prefer it.

Big projects still get complicated fast

Large software projects create their own complexity, with inter-dependent
libraries, long test cycles, hard deployment processes and a multitude of
people each working on their own bit of the solution. That's even before
the deadlines loom close, the integration problems become insurmountable,
weekends become indistinguishable from weekdays in terms of workload and
half the team stops talking to the other half. Ant may simplify the
build and test process, and can eliminate the full time "makefile engineer"
role, but that doesn't mean that someone can stop "owning the build".
Being in charge of the build has to mean more than they type "ant all" on
their system, it means they need to set the standards of what build tools to
use, what the common targets, what property names and files should be
and generally oversee the sub projects build processes. On a small project,
you don't need to do that - but remember: small projects become big projects
when you aren't looking. If you start off with a little bit of process, then
you can scale it if needed. If you start with none, by the time you need
it will be too late.

You still need all the other foundational bits of a software
project

If you don't have an source code management system, you are going to end
up hosed. If you don't have everything under SCM, including web pages,
dependent jars, installation files, you are still going to end up hosed,
it's just a question of when it's going to happen.
CVS is effectively free and works well with Ant, but Sourcesafe, Perforce,
Clearcase and StarTeam also have Ant tasks. These tasks
let you have auto-incrementing build counters, and automated file
update processes.

You also need some kind of change control process, to resist
uncontrolled feature creep. Bugzilla is a simple and low cost tool for
this, using Ant and a continuous test process enables a rapid evolution of code
to adapt to those changes which are inevitable.

End piece

Software development is meant to be fun. Being in the maelstrom of a
tight project with the stress of integration and trying to code
everything up for an insane deadline can be fun - it is certainly
exhilarating. Adding a bit of automation to the process may make things
less chaotic, and bit less entertaining, but it is a start to putting
you in control of your development process. You can still have fun, you
should just have less to worry about, a shorter build/test/deploy cycle
and more time to spend on feature creep or important things like skiing.
So get out there and have fun!

Steve Loughran is a research scientist at a corporate R&D lab,
currently on a sabbatical building production web services against
implausible deadlines for the fun of it. He is also a committer on
Apache Ant and Apache Axis, and co-author of
Java Development with Ant.
He thinks that if you liked this document you'll love that book because
it doesn't just explain Ant, it goes into processes, deployment and best practices
and other corners of stuff that really make Ant useful. (It would
have been easier to just rehash the manual, but that wouldn't have been
so useful or as much fun).